This invention relates to photographic cameras having an electromagnetically operated shutter, and more particularly to a device for protecting film in the camera against fogging that is adapted for use with a shutter control circuit in which an actuating pulse temporarily energizer a magnetic solenoid to control the closing movement of the shutter.
It is known to provide Prior Art various types of shutter control circuits including one in which the duration of an actuating pulse for energizing a magnetic solenoid is controlled in accordance with a preselected or computed shutter time. However, when the circuit is damaged and fails to produce an actuating pulse, or when the actuating pulse does not produce sufficient power to energize solenoid to retain the closing member of the shutter in cocked position the closing member follows the opening member and produces a blank or wasteful frame exposure; this situation can arise as a result of damages either to the solenoid which connects the circuit, output is or the cooperation of the solenoid with the armature because through the introduction of foreign particles into the space is interrupted or the circuit's between the solenoid and the armature battery supply is short circuited, or through a decline in the actual voltage of the battery, the closing member. It often happens, moreover, that the operator is not immediately aware of this fact.
Another type of shutter control circuit produces an actuating pulse of predetermined short duration that temporarily energizes the solenoid, to attract or repel the armature depending upon whether or not a permanent magnet is employed. When the shutter malfunctions from any one of the above-mentioned reasons, a fogged frame of film will result because the shutter will remain open after the actuating pulse is produced. Even if the operator is aware of faulty shutter operation, it is nevertheless likely that the operator will, in the future overlook closing the shutter as a necessary prelude to resetting the camera. With the shutter left open, and the film winding lever or rewinding crank is operated, the fresh or exposed area of the film will be fogged. This is particularly serious if the camera is operated by means of a motor drive unit.
To improve the reliability of the camera drive control, be it manual or automatic, it is necessary that (1) the operator is warned through a visible signal that something is wrong, (2) the film winding and rewinding mechanism is automatically hindered from further movement in response to any one of the above mentioned malfunctions; and (3) the closing member of the shutter can be disconnected from the latching connection through an operating member that is accessible from the outside of the camera housing, and actuating the closing member release monitor the operator to wind or rewind the film.